-matrices, discrepancy and preservers
Let and be positive integers, and let and be nonnegative integral vectors. Let be the set of all -matrices with row sum vector and column vector...
Let and be positive integers, and let and be nonnegative integral vectors. Let be the set of all -matrices with row sum vector and column vector...
The simple incidence structure formed by points and unordered pairs of distinct parallel lines of a finite affine plane of order is a design. If , is the complementary design of . If , is isomorphic to the geometric design (see [2; Theorem 1.2]). In this paper we give necessary and sufficient conditions for a design to be of the form for some finite affine plane of order . As a consequence we obtain a characterization of small designs .
There is described a procedure which determines the quasigroup identity corresponding to a given 3-coloured 3-configuration with a simple edge basis.
We consider two classes of latin squares that are prolongations of Cayley tables of finite abelian groups. We will show that all squares in the first of these classes are confirmed bachelor squares, squares that have no orthogonal mate and contain at least one cell though which no transversal passes, while none of the squares in the second class can be included in any set of three mutually orthogonal latin squares.